1. Field of the Invention
This invention relates in general to the construction of valves and in particular to a new and useful valve for high and maximum pressures and two separately operable control levers for effecting the opening thereof.
2. Description of the Prior Art
Shutoff valves which are particularly useful for high pressure devices such as spray guns are known in various forms and particularly those which consist of a differential piston which is driven by a pressure medium in the form of a liquid or gas to be shut off and which works in a cylinder of the valve housing between the inlet and the outlet passages for the pressure medium. Such a valve operates against a seal associated with the outlet passage and it is controlled by a control piston which is arranged on the inlet side or downstream side ahead of the differential position in a common pressure chamber therewith. A throttling zone leads from the inlet range of the differential piston into the pressure chamber formed between the outer wall of the piston and the cylinder. In a known embodiment a differential piston has an axial through-bore with a valve seat arranged on the side opposite the seal for the differential piston and which is provided for the control piston and which is adjustable by means of a control mechanism. If the control piston is in a closing position, it is pressed against the valve seat by the differential piston for closing the axial through-bore. To this end the control mechanism has a piston rod connected to the control piston which is surrounded by a compression spring which admits the control piston. Consequently the closing force in such a construction results from the spring force of the respective compression spring which is employed. This in turn leads to a relatively great opening and holding force which must be expended by the operator of any device employing it such as a spray gun.
The present invention as already suggested in another application which has not become part of the state of the art that the differential piston be separated from the control piston by a pressure chamber and that the control piston is like the differential piston in a closing position due to the pressurization by the pressure medium from the outside of the pressure chamber and exposes a bypass arranged in the valve housing and opening into the outlet behind the seal in the direction of flow after it has been forced back into the opening position by means of a control mechanism. Both the embodiments have the disadvantage that the control mechanism does not provide an adequate safety since the installation of such a shutoff valve in a high pressure spray gun perm its actuation of the gun with only one hand. The other hand remains free and this is not without risk considering the fact that the high pressure spray guns work with very high and maximum pressures and can result in injuries to the operator.